One Experiment to Another
by Tenebrielle
Summary: Steve Rogers wasn't the only Avenger exposed to the Super Soldier Serum.


_A/N: Written as a gift for the lovely and talented Inkspire, as part of the Beta Branch's Secret Santa one-shot gift exchange! :) _

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**One Experiment to Another**

Steve Rogers wasn't a nervous guy. He never had been, not even while lying through his teeth to try to enlist. Not even seventy-odd years removed from his time, when he had every right to be unsure of himself at all times. That wasn't to say the adjustment was easy, but he tried to handle it with a sense of humor and a notecard taped inside his shield like when he'd entered the alien world of show business in 1942. At least in public.

So the fact that just _standing _next to some scientist while waiting for an elevator turned him into a ball of nerves really bothered him.

Okay, so maybe ball of nerves was an exaggeration, but Steve liked things to be black and white and things _never_ seemed to be black and white when it came to Dr. Bruce Banner. He glanced to his left and received a slight smile from the scientist. Steve nodded in acknowledgement and bounced a little impatiently on the balls of his feet.

It wasn't that Banner was particularly intimidating. Outside of the lab, Banner was the kind of guy who stuck to the edges of a room, quiet and a little shy, and with a touch of wariness that Agent Coulson attributed to being hunted by the military. He was friendly enough once you got him talking, though, and Banner really came out of his shell when he was on his own turf. Steve actually had developed a little bit of a soft spot for the guy. His glasses and his soft voice reminded Steve of another kindly doctor from what didn't feel like very long ago.

The elevator chimed and the immaculate chrome doors opened. Steve followed Banner inside. Romanoff still wouldn't ride in the same elevator as him. Steve didn't blame her, but he liked to set a good example for the team. He fumbled in his shirt pocket for his leather covered agenda, just for something to do. The little notebook had been a gift from Agent Coulson, who understood (unlike Stark) that Steve didn't need to use electronic devices for everything.

The agenda slipped from his fingers and fell to the floor. Steve lunged after it, but missed. Banner bent to retrieve it. He handed it to Steve with a sheepish smile. "It's a good idea," he said. "This thing."

Steve accepted the notebook and slipped it back in his pocket. "I guess."

"I mean," Bruce continued, one of his thumbs tracing over his knuckles. "Using a paper one instead of your phone. Phones get dropped, run out of battery, hacked…hard copies make a lot of sense."

"I'd honestly forgotten a telephone could do all that these days," Steve said, drawing a smile from the scientist. He was growing used to the solid weight of the cellular telephone in his trouser pocket. At first, he kept losing it around the apartment, or forgetting it when he went out, but a notecard on the door solved that.

"How's it going with that?" Bruce asked. He'd actually been one of the more helpful people to come to with questions about the phone's dizzying array of features. Stark just couldn't seem to wrap his mind around the fact that technology wasn't intuitive to everyone. "Better, I hope?"

"Yeah, actually," Steve replied. Now that he had learned how to use the cell phone, it was one of his favorite things about 2012. He still marveled over the fact that it was a camera, too. A camera (with a _flashbulb_ even!) that could fit into his trouser pocket. It was sure something else. "I still don't get the point of texting. If it's so easy, why not just _call_?"

Banner chuckled and they fell back into silence. Steve studied him out of the corner of his eye. The physicist absently fiddled with his watchband, oblivious to Steve's scrutiny. It had taken Rogers the better part of a week to finally pin it down.

The thing was, Banner wasn't just _Banner_. Steve would have never guessed that the unassuming scientist shared a body with a huge green monster nicknamed the Hulk just based on physical appearances. According to Bruce and SHIELD's files, he transformed into this rage monster whenever he lost his temper, was physically threatened, or injured. Steve didn't know all the specifics, but he knew enough to make a point of _not_ setting Banner off.

Even the Hulk situation wasn't black and white, though. Steve had seen the Hulk half-destroy the helicarrier, but he'd also seen the monster follow orders. And there was no denying he'd saved Stark's life during the Battle of Manhattan. It wasn't the Hulk that made Steve nervous.

No, it was the fact that Bruce Banner had become the Hulk by accident…while trying to reproduce the Super Soldier Serum that had created Captain America. His stomach twisted uncomfortably at the thought. The only other person Steve had ever been around who'd been exposed to anything like it was the Red Skull, and everyone knew how _he_ had turned out. Banner sure seemed pretty well-adjusted in comparison, Hulk and all.

He bounced again on the balls of his feet while the elevator zoomed upward. Steve knew his face wouldn't betray his thoughts; he'd been in the Army long enough to develop a parade ground poker face when he needed it.

During the war, things had happened so fast that Steve could barely keep up with anything that wasn't an immediate problem. Between the chaos surrounding his transformation, the tour, and then the actual _battles_, he'd hardly been able to catch his breath, let alone process anything that had happened to him. Steve managed to catch himself before he snorted. Or so the shri-_psychologists_ at SHIELD assigned to help him with the transition kept telling him.

It wasn't their fault they didn't know anything. How could they, if Steve himself didn't? He knew a lot about the physiological issues that came with his transformation, some through preparation with Dr. Erskine and others, some through just plain experience. He could bench a motorcycle and throw that shield around like nobody's business. He had to eat a lot more just to maintain his weight (gaining was nearly impossible), and his crazy metabolism still wouldn't let him get drunk. But the rest? Steve hadn't thought about it. He could do the impossible, and during the war, that had been enough.

At the time he hadn't realized just what that wacky metabolism would do, other than let him shrug off wounds in a couple of days that should have taken weeks or months to heal. That had been convenient. Faster healing meant Steve could take more missions and save more lives. The news that it would also mean he would age much slower than everyone else was meaningless. They were in the middle of a _war_. There was a very real chance that he or any of the Commandos could die at any time. It had been impossible to think about the future when none of them was really sure they'd live to see next Christmas.

Steve had had a lot of time to think about it lately. Turned out it was pretty lonely being one-of-a-kind. He didn't regret his choice, not exactly, but during his many sleepless nights he often wondered if he would have made the same choice, if he'd known what was coming, staring eternity in the face-

The soldier couldn't hold back the soft snort this time. He was being melodramatic again, and that was just a waste of time. Banner shot him a questioning look, but the elevator chimed for his floor before he could say anything. The scientist nodded at him as the doors opened and stepped out. Steve watched his retreating back for a moment, warring with himself.

When he'd found out about Banner, exactly _how_ he'd made himself into the Hulk and what he'd lost in the process…and well, maybe it was awful of him, but suddenly Steve hadn't felt so alone. That little glimmer of hope had been enough to raise so many questions. Had Banner known what he was signing on for when he tested his serum? Why had he done it? Did he blame Steve for his accident?

Yet Steve was honestly afraid to bring it up. Stark might crack wise about Bruce's condition, but _he_ wasn't a living reminder of everything Banner had tried, and failed, to achieve. Everything he had lost. The memory of his confession on the helicarrier was still all too fresh in Steve's mind. It had colored all his interaction with the scientist afterwards, as much as he tried not to let it. The last thing Steve wanted to do was make things worse for Banner. So he bit his lip to keep the questions from bursting out and carried on.

The chrome elevator doors began to close. Steve bit his lip again, hesitating.

Indignant anger suddenly burst in his chest. This was not how Steve Rogers handled problems. He didn't _hide_ from them; he hit them head-on! If he wanted answers, he was going to have to just man up and ask some questions. He was going to have to trust that Banner wouldn't take things the wrong way.

"Doctor Banner!" he called after the scientist. Banner jumped and looked over his shoulder. Quickly, Steve jammed his hands between the elevator doors and pushed. They retracted instantly with a screech of metal and whine of gears. Oops, maybe he'd pushed a little too hard.

"You got a minute?" Steve asked. He straightened up and stepped out of the elevator with a sheepish smile.

Bruce blinked. He looked a little surprised by Steve's sudden request. "Uh, sure," he replied. His eyes darted to the damaged elevator doors before returning to Steve's face. "I'm going to the lab; is that okay?"

"Long as you don't mind me tagging along."

"Not at all."

He hadn't really been to this part of Stark Tower before, Steve thought while they walked. He didn't really like the labs much; they always made him feel a little bit stupid and hopelessly out of place. But that had always been with Stark, and Stark didn't exactly go out of his way to make it a pleasant experience. Maybe Banner would be different.

Banner's lab was in the curving "nose" of Stark tower, with a lot of big windows. Even from the outside it seemed a little friendlier than Stark's cavernous workshop. Something tinkled musically as they entered, and Steve looked up to see a small set of chimes hanging above the door. He raised an eyebrow at Banner.

"It's not good for people to surprise me," the scientist explained, his dark eyes twinkling a little. Steve grinned while he followed him through the array of workbenches. Banner casually tossed his jacket on what had to be his desk and dropped into his chair. "So what's on your mind?"

There was another chair nearby that looked like it had never been used, near a deliberately bare spot on one of the tables. Steve suddenly felt too awkward to sit, so he leaned against the table as nonchalantly as he could. His chest was beginning to tighten with nerves again. He could still abort; pretend like he just had a question about his phone or something. His fingers even twitched at the thought. But that wasn't how Steve Rogers did things. He swallowed and took the plunge.

"Why?" he started, kicking himself for hesitating. "Why'd you do…it?"

_Great. Very articulate, Rogers, _he thought sourly, but Banner didn't need to ask what he meant. He studied Steve for a moment, his smile slowly fading. He took off his glasses and methodically polished them on the edge of his shirt. When he looked up again, he somehow looked older. Tired, even.

"Interesting," Banner observed quietly. "You're the only one who's asked me that question in a long time. Well, other than me, anyway. I mean, who _wouldn't_ want superpowers?"

A hint of bitterness tinged the end of the sentence, and Steve swallowed nervously. This hadn't been a good idea. "Sorry," Steve apologized. His resolve vaporized, and for a moment, he was ten years old and standing in Sister Mary Francine's office again. "I-I didn't mean-"

"Steve, it's fine," Bruce interrupted. He smiled a little tiredly at the soldier. "You should know. Especially if we're going to be working together in the future." He shrugged. "It's not like there's anyone else you could ask."

Steve didn't say anything. A pang of loneliness lanced through his heart, but he was encouraged by the fact that he was going to get some answers. He settled onto the edge of the table, looking expectantly at Banner.

"I wasn't trying to, uh, take up your shield or anything," Banner said dryly. His eyes twinkled humorously, and Steve couldn't help smiling a little. Tension he didn't know he was carrying drained out of his chest. It was a relief, in a weird way, to know that. "I mean, what lonely little kid wouldn't want to be Captain America? But I can assure you that wasn't my primary goal."

"Agent Coulson told me you were trying to recreate the Super Soldier Serum," Steve said. "Weren't you?"

Banner shrugged. "Coulson may have glossed over a few details."

"He does that," Steve observed, matching his dry tone, and Bruce smiled.

"Technically, this is all still classified," he started, leaning back in his chair. It was a casual gesture, but Steve could see the tension around his tired eyes. "But as one experiment to another, I think I can make an exception. Yes, I was told I was working on something else. But once I got deeper into the project, found the old notebooks from the '40s…well, it didn't take a genius to figure out what I was _really _working on." Banner paused for a moment, as if weighing his words. "Unlocking the secret behind your body's enhanced regenerative capabilities could do a lot of good for a lot of people, Steve. Protection against radiation was just one example. I wasn't naïve enough to pretend there weren't battlefield applications for my work, but I hoped that the good it would do when the technology eventually trickled down to the civilian population would make up for it."

Steve looked at his hands, suddenly very conscious of the bulge of his muscles against the fabric of his sleeves. He still remembered vividly what it was like to be trapped in a failing body, and he was a little ashamed he hadn't really ever thought of the project like that. Like a cure.

"They didn't know as much about radiation in 1942 as we know now," Banner continued. He sounded like a professor now. "They were learning quickly, but the field was still very young. I thought that maybe Doctor Erskine's vita-rays might actually be gamma rays. We knew the formula worked, you're proof of that, Steve, but the vita-ray source was the piece we were missing. After Erskine died, Howard Stark was the only one who knew…and to my knowledge, he destroyed all that work sometime after you went missing."

Erskine. Howard Stark. Steve's stomach jolted at the casual use of his friends' names. He swallowed hard. Banner didn't mean any harm, it just wasn't…yesterday for him.

"We were just getting ready to start testing on mice. But I…decided to take a shortcut."

"But _why?_" Steve asked, confused. He'd made a similar choice, taken a similar risk, but hell, the world had been at _war_. Banner had just been working in a lab. "If it was untested…"

Banner's face fell. He sounded pained. "I was going to lose my funding, Steve, if I didn't have results, _real_ results, for General Ross to show his superiors. We were already in a precarious situation, because Ross was the head of the program and I was, uh, romantically involved with his daughter at the time. We'd started dating before I got the grant. My lab was under extremely close scrutiny as a result; we didn't get any of the leeway other labs got, due to that connection."

It took him a moment to realize what Banner meant. He felt his jaw drop. "You did it for _money_?" Steve exclaimed. He felt a little sick, and his skin crawled at the idea that _he_ had somehow inspired someone to this.

"Not in the way you think," Bruce said quickly. He sighed, suddenly looking overwhelmed. "Look, losing my funding wouldn't have just affected me; it would have affected everyone in the lab. My co-investigators, our students, even the lab techs, were all depending on me keeping that money."

Steve stiffened as a chill raced down his spine. This was something he could understand better than most: sacrificing oneself for the sake of others. "So you skipped the mice and tested it on yourself," he observed.

"Pretty much," Banner confirmed with a rueful little shrug. His eyes fell to his hands, where his thumb was tracing anxiously over his knuckles. "Not the, uh, best decision I've ever made."

"You had good intentions, though," Steve told him. He wasn't sure if he was trying to reassure himself or the scientist. "You didn't want to let them down."

But, no, nothing could ever be black and white with Bruce Banner. The scientist shot him a pained look. "What I did wasn't _noble_, Steve," he said bitterly. "I tested the serum on myself because I didn't think I could fail." He laughed humorlessly. "I thought the worst that could happen was that it _wouldn't_ work. Best case, I got to be Captain America. Not a bad tradeoff for five more years' job security."

Steve's insides squirmed a little, and he felt his shoulders slump. Part of him was disappointed that, no, Banner didn't have all the answers he was looking for. But another small part of him was relieved, too. Bruce didn't blame him; didn't blame anyone but himself for the accident. Steve might not have his answers, but at least he wasn't the only one. "You had no idea what you were getting into, did you?" he observed.

A shadow passed over Banner's face in the moment he weighed his reply. "The serum brought out the best in you, Steve," he said hollowly. "I'm still not sure what it brought out in me."

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